Modal liquid crystal lenses are switchable lenses with a continuous phase variation across the lens. Modal liquid crystal lenses have been described, for example, by A. F. Naumov in a publication entitled Control Optimization Of Spherical Modal Liquid Crystal Lenses, published in Optics Express (26 Apr. 1999/vol. 4, No 9). The basic design of a modal liquid crystal lens, according to Naumov, is illustrated in FIGS. 1a and 1b. FIG. 1a is a planar view of an illustrative electrode layer used in a modal liquid crystal lens, and FIG. 1b is a side sectional view of an illustrative modal liquid crystal lens. As shown in FIGS. 1a and 1b, modal liquid crystal lens 100 includes a control electrode 130, which consists of a low conductivity, or highly resistive layer of conductive material, such as indium-tin-oxide (“ITO”), for example. Control electrode 130 is surrounded by a highly conductive annular contact electrode 120, which is made from a conductive metal, such as silver, aluminum, copper, for example.
FIG. 1b illustrates the construction of modal liquid crystal lens 100. As described by Naumov, control electrode 130 generally has a relatively high resistance with a surface resistance of around a few MΩ/square. Ground electrode 160 is generally a highly conductive ITO layer with a surface resistance of about 50 to 200 Ω/square. The cell 150 containing the liquid crystal material is formed by the spacers 140 placed between the front substrate 110 and rear substrate 170. The modal liquid crystal lens 100 is operated by applying a voltage to the annular contact electrode 120. The voltage across the modal liquid crystal lens 100 decreases radially towards the center of the modal liquid crystal lens 100 because of the potential divider that is formed by the high resistance control electrode 130 and the capacitance of the liquid crystal layer 150. In response to the radially varying potential, the retardance of liquid crystal layer 150 changes. Thus, the optical path length through the liquid crystal layer 150 increases from the edge of the modal liquid crystal lens 100 towards the center thus producing a retarding profile across the modal liquid crystal lens 100. By controlling the voltage and frequency of the waveform applied to the annular contact electrode 120 the optical power of the modal liquid crystal lens 100 can be continuously adjusted over a range of a few Diopters, depending on the thickness of the liquid crystal layer 150.
While such modal liquid crystal lenses offer several advantages in terms of continuous optical power tuning and simplicity of design, they have several limitations that hinder their practical use as spectacle lenses, in particular, a lens for the treatment of presbyopia. For example, such lenses are not completely transparent, and use visible metallic electrodes. In addition, such lenses are not constructed in a manner that allows for them to be cut and shaped so that they may be placed within a frame. Moreover, such lenses do not have a relatively quick response time (for example, less than 30 milliseconds) so that the optical power changes faster than the wearer's eye can detect, and do not account for a step change in optical power with an adjacent base lens used to provide a distance correction. This leads to discomfort for the wearer, and also detracts from the cosmetic appearance of the lens.
Accordingly, the present invention provides an electro-active lens and electro-active spectacles useful in the treatment of presbyopia that employ modal liquid crystal lenses, and that overcome the disadvantages of known devices while offering features not present in known devices. Although certain deficiencies in the related art are described in this background discussion and elsewhere, it will be understood that these deficiencies were not necessarily heretofore recognized or known as deficiencies. Furthermore, it will be understood that, to the extent that one or more of the deficiencies described herein may be found in an embodiment of the claimed invention, the presence of such deficiencies does not detract from the novelty or non-obviousness of the invention or remove the embodiment from the scope of the claimed invention.